Well, he says so himself: This is probably the most provocative hypothesis I have ever (and will ever) advance: The long-term increases in carbon dioxide concentration that have been observed at Mauna Loa since 1958 could be driven more than by the ocean than by mankind’s burning of fossil fuels. Most, if not all, experts in the global carbon cycle will at this point think I am totally off my rocker. Hmm, this pic applies (it can’t be rude, its Egyptian :-).
This isn’t an interesting idea, or a procovative hypothesis, its just w*nky (don’t worry, that link isn’t rude). Why? Well, you can try #5 on this list of myths if you like, and the refs to RC therein. There are all kinds of reasons why we know it, but the one I like best, that avoids having to know about C13 and stuff, I’ll copy from waht I wrote earlier: “To believe this, you have to believe that CO2 and other GHG’s were stable at pre-industrial concentrations for thousands of years, then suddenly, just as humans started emitting them, some natural process started emitting them, while at the same time removing from the atmosphere an equivalent quantity of the man-made GHGs”.
And no, I’m not going to deconstruct Spencers argument in detail, because I haven’t bothered read it. Why would I? Any more that reading the latest astrology or flat-earthism.
[Update: as G points out, the comments are worth reading, even if the post isn't. Courtney is mad enough to want to claim priority on this nonsense, apparently he fooled the easily-fooled E&E into publishing it in 2005. Even funnier, he comes close to accusing Spencer of plagiarism: There are some surprising similarities between Dr Spencer's article and my presentation. For example, his Figure 3 presents the same data in the same way as my Figure 1, and he draws the same conclusion from it as we do in our paper. I run out of adjectives to describe his later assertion that "there is no "build up" of CO2 in the atmosphere.".
As FE points out in the comments there, another nice piece of evidence ignored by the wackos is the decline in O2 levels, which... oh well, they aren't listening -W]